A) Field of the Invention
This invention relates to a charge coupled device and a solid state imaging apparatus, and especially relates to a charge coupled device arranged linearly of which channel is diverged near an edge and a solid state imaging apparatus using that.
B) Description of the Related Art
FIG. 9 is a schematic plan view of a conventional charge coupled device 60.
A charge coupled device (CCD) 60 that is arranged linearly and of which channel is diverged into two lines near an edge is consisted by including floating diffusions (FD) 5, each of which is positioned at each end of the CCD 60 after divergence and detects the transferred signal electric charge. Moreover, the charge coupled device (CCD) 60 has reset transistors RS1 and RS 2 draining the detected signal electric charge at desired timing and a reset drains RD after the FD 5.
The CCD 60 is a two-phase driving type CCD and is consisted of two phases (φH1, φH2) of electrodes (a first layer electrode 7 and a second layer electrode 8) and transfer channels 3 and 4. The transfer channel 3 under the first layer electrode 7 is formed to have deeper electric potential than the transfer channel 4 under the second transfer layer electrode 8, and the signal electric charge is temporally stored in the transfer channel 3 at a time of transferring the signal electric charge.
FIG. 10 is a diagram showing electric potential of the impurity layer 3 in the conventional charge coupled device 60 cut in a line E-F shown in FIG. 9.
As shown in the drawing, since length in a transfer direction of the CCD is almost uniform, electric potential in a direction crossing at a right angle with the transfer direction of the CCD in the impurity layer 3 is approximately flat, and the signal electric charge to be accumulated is distributed in a wide area.
Moreover, for details of the prior art, Japanese Laid-Open Patent Hei5-308575 is referenced.
FIG. 11 is a schematic view showing movements of the signal electric charges in the channel formed on the impurity layer 3 in the conventional charge coupled device 60.
As shown in the drawing, the signal electric charges in the impurity layer 3 are widely distributed, and it takes a long time to transfer them to a diverged channel. Moreover, the transfer by the thermal diffusion contributes in a flat electric potential and the electric potential is in proportion to the square of the distance.
As described in the above, if the transfer time is long at the diverged part, the solid state imaging apparatus should be driven at predetermined transfer frequency in a case that the conventional charge coupled device is used as a horizontal CCD of the solid state imaging apparatus. For example, if the transfer is not completed during the predetermined time, it will degrade transfer efficiency.
Therefore, for example, if the charge coupled device 60 is used as the horizontal CCD of the solid state imaging apparatus, horizontal flow of an image and degradation of resolution will occur. Moreover, if a color filter is laminated on a photodiode to obtain a color signal, color artifact signal may be generated.